1. Field of the Invention
The present invention relates to a filter component with a passive element, which includes an elastic wave filter including an elastic wave resonator, and also to a radio-frequency module including the filter component.
2. Description of the Related Art
Hitherto, a radio-frequency module 500 shown in FIG. 15 is known (see, for example, Japanese Unexamined Patent Application Publication No. 2013-31030 (paragraphs 0012 to 0037, FIGS. 1 to 7, Abstract, etc.)). The radio-frequency module 500 is a module mounted on a mother substrate included in a communication mobile terminal such as a cellular phone and a mobile information terminal. The radio-frequency module 500 includes a module substrate 501. In accordance with the required functions of the radio-frequency module 500, circuit elements, for example, various electronic components such as a filter component 502 (duplexer) and a switch IC, various electric circuits such as a matching circuit and other filter circuits, various passive elements such as inductors, capacitors, and resistors, are selected and are mounted on the module substrate 501. The filter component 502, a chip passive element component for forming a matching circuit, and various other electronic components are mounted on mounting electrodes 501a provided on the mounting surface of the module substrate 501.
The filter component 502 has a wafer level-chip size package (WL-CSP) structure, and includes a filter substrate 503, an insulating layer 504, a cover layer 505, and an elastic wave filter 506 having comb-shaped electrodes (IDT electrodes).
The filter substrate 503 is a piezoelectric substrate made of a piezoelectric substance such as lithium niobate, lithium tantalate, or quartz. Plural elastic wave resonators 506a constituted by comb-shaped electrodes and reflectors made of Al or Cu are provided in a predetermined region 503b of one main surface 503a of the filter substrate 503. The plural elastic wave resonators 506a are combined to form the elastic wave filter 506 (surface acoustic wave or SAW filter). The elastic wave filter 506 includes a transmit filter that transmits signals and a receive filter that receives signals.
The insulating layer 504 surrounds the predetermined region 503b of the main surface 503a of the filter substrate 503, and the cover layer 505 is disposed on the insulating layer 504 so as to form, together with the insulating layer 504, a surrounded space between the filter substrate 503 and the cover layer 505. The elastic wave filter 506 is disposed in this space.
Plural external-connecting terminal electrodes 507 pass through the insulating layer 504 and the cover layer 505 and are exposed on a main surface of the cover layer 505. The terminal electrodes 507 are electrically connected to the elastic wave filter 506. The filter component 502 is disposed such that the cover layer 505 opposes the mounting surface of the module substrate 501. The filter component 502 is electrically connected to mounting electrodes 501a on the mounting surface of the module substrate 501 via solder bumps H formed on the respective terminal electrodes 507.
The module substrate 501 is a multilayer substrate constituted by plural insulator layers stacked on each other. As a result of forming via-conductors and in-planar conductive patterns in the insulator layers as required, a wiring electrode 508 is formed in the module substrate 501. At least a portion of the wiring electrode 508 forms various passive elements P, such as an inductor for adjusting the characteristics of the elastic wave filter 506 and a capacitor and an inductor for forming a matching circuit, which are electrically connected to the filter component 502 (elastic wave filter 506).
For the actual use of the elastic wave filter 506 including the elastic wave resonators 506a, a passive element P, such as an inductor, is connected to the elastic wave filter 506 to adjust the filter characteristics. For example, if the filter component 502 having a WL-CSP structure is bare-chip-mounted on the module substrate 501, the passive element P constituted by the wiring electrode 508 within the module substrate 501 is connected to the elastic wave filter 506 included in the filter component 502, as shown in FIG. 15. Forming of the passive element P in the module substrate 501 makes the module substrate 501 thicker, and the height of the radio-frequency module 500 including the module substrate 501 on which the filter component 502 is mounted is accordingly increased.
It is known from simulation analysis results that the thickness of the single-layer filter substrate 503 necessary for forming the elastic wave resonator 506a on the main surface 503a is about five or six times as large as the pitch of comb-shaped electrodes. The pitch of the comb-shaped electrodes is set in accordance with the resonant and anti-resonant frequencies of the elastic wave resonators 506a. The pitch corresponds to half the wavelength, and the typical pitch of a 2 GHz-SAW filter, for example, is about 1 μm. In the related art, however, to improve the handling characteristics of the filter component 502 when being bare-chip-mounted on the module substrate 501 and to prevent cracking or chipping of the filter substrate 503, the filter substrate 503 is formed very thick, for example, at a thickness of 100 μm or greater. In a 2 GHz-SAW filter, for example, the filter substrate 503 is formed at a thickness of about 100 times as large as the pitch of the filter. The filter substrate 503 is formed excessively thick. This increases the height of the radio-frequency module 500 including the filter component 502 mounted on the module substrate 501.